Frequency converter



April 13, 1943. w w o 2,3l6;610

FREQUENCY CONVERTER Filed July 24, 1941 INTERMEDIATE I FR Equ ENCY CIRCUITS.

Inventor: William W Moe,

His ttorney Patented Apr. 13, 1943 UNITED STATES than .FREQUENGY CONVERTER William Moe, Bridgeport, Conn, assignor-to General Electric Company, a corporation of New York Application July 24, 1941, Serial .No. 403,799

2. Claims. (01. 250-29 gMy invention relates to frequency converters such as are commonly used in radio receivers to convert the frequency of received oscillations to oscillations having a common or intermediate frequency.

It has for one of its objects, to effect certain improvements in such converters with respect to means for maintaining proper voltage at the converter of the frequency of the local oscillator over'the range offrequencies to be received.

Another object of my invention is to provide an improved coupling arrangement between the local oscillator and converter to' transfer voltage to the converter of constant intensity at all frequencies over which the oscillator is tunable.

'Still another object of my invention is to effect certain improvements in the circuit of the local oscillator whereby its intensity of oscillations generated my be maintained at desired values at'difierent parts of the tuning range.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention, itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure represents an embodiment of my invention.

Referring to the draWing,;I' have represented therein an antenna I arranged to intercept oscillations tobe received and which is coupled by means of a transformer 2 to the input circuit of an electron discharge converter 3. Oscillations generated by the local oscillator i are also supplied to the input circuit of the converter 3 to combine with the received oscillations and produce' in the output circuit of the converter oscillations of constant frequency for all frequencies to be received. The output circuit of the con- .verter 3 is represented by the rectangle which may comprise the intermediate frequency amplifiers and selective circuits of the receiver in Which my. invention is incorporated. Since these circuits are of conventional construction they require no description here.

Operating potential for the anodes of the discharge devicest and 4 may be considered as in- ,cluded Within the rectangle 5 and supplied to the anodes of these devices through conductors represented bythe connecting lines on the drawing.

The anode of the discharge device 4 .is concted to ;ground,,.througha largev by-p denser 6 and thence through a frequency deteryed the. ante n mining circuit lv and'grid condenserfi to the control. electrode of thisidischar ge device. The circuit fl .comprises an inductance which may comprise the. series connected; sections. 9,. l-iland] l and-Which comprises capacitances i2 and I3.

The condenser; I 2 .may be variablefor tuning the oscillator-over the 'des'iredlb'and .of frequencies. It. is. connected across -the total inductancei9, ,l 0, and-l l of circuit]. Condenser l3 maybe a fixed condenser or one that is variableffor purposes of .initialfladjustment. It is connected across .in-

ductan'ces 9 and I!) of circuit 1'.

Jlhe. tuned input circ'uitof the'con-verter 3 cornprisesthe secondary windingfi of thetrans- 'fo1:meri. 2, which is .connected between theciontroLelectrode. i l of thelconverterand a point. on

the oscillatory circuit! between. inductances f9 and..." to, fand'. it also comprises the. tuning condense'rfit connectedlbetween the control electrode. 14 and ground; thistuningcondenser being .-arranged .to be unicontrolled with condenser t2 of the oscillator ,by means represented loy the dotted line. I l

he lconverter 3 15 provided -with thecusu al cathode .biasresistor I8 which isshunted bythe lt will be seen that as thus connected that portion of the frequency determining. circuit Lof thelocal oscillator comprising the inductances it and llis includedinthetuned circuitsl5, l6 of; the converterfi in; serieswith the condenser l6; and theindu tance IS. ;l '.1:1at. is,-the tunedinput circuit of the converter 3 comprise s thellinductance l5 inductanceslil and ll andthe tuni ceenelee th t e n n e 2 si n f uen e w t th e e I5. .1 an i ion c an tun n th .eenr r whereb the combi wi t rece ve sc llat ons: ,te p odu i t .euinu ci cu t 5 re th eeny rt i .int rmed ete r 1 1.

eas e z-te cnieeee e es f a i t eu ne ,It. is desired,.in order to -obtain -efficientirequency conversion in the converter tube ii/that frequency. Thus the circuits are tuned nearer to the same frequency on a percentage basis at the upper end of the hand than at the lower end of the band. This means that the transfer of oscillations from the local oscillator through the network comprising the inductance I5 and the condenser I6 is more efficient at the upper end of the band than at the lower end of the band, thereby tending to increase the voltage between the control electrode I4 and cathode of the converter in the higher frequencies. At the same time, as is characteristic of most oscillator circuits, the oscillator I4 oscillates more strongly at the higher frequencies than at the lower frequencies, thereby likewise tending to increase the intensity of oscillations supplied to the converter. These oscillations, however, are supplied from the two inductances I0 and II. These inductances are so arranged in the circuit with respect to condensers I2 and I3 that the voltage thereon may be adjusted to vary in proper relationship to maintain the voltage between control electrode I4 and cathode 20 substantially constant over the band.

In initially adjusting the system for operation the condensers I6 and I2 may be adjusted for operation at the high frequency end of the band. At this frequency very little current flows in condenser I2 or inductance II. The inductance I0 may then be adjusted to produce oscillations between the control electrode I4 and cathode 20 of the proper intensity at the highest frequency in the band. The condensers I6 and I2 may then be adjusted for operation at the lowest frequency in the band. This tends to reduce the voltage on coil I0 because of the fact that the oscillator oscillates less strongly at the low frequencies than at the high frequencies. However,

because of the increase in current in condenser I2, as the capacity is increased, the voltage on inductance II through which this current flows also increases. This inductance II may then be adjusted to produce the proper voltage between the control electrode I4 and cathode 20 of the converter. This adjustment does not, to any substantial extent, affect the first adjustment at high frequencies because very little current flows in capacitance I2 at the high frequencies. If it does aifect it, condensers I6 and I2 may again be adjusted for high frequency and the inductance I0 readjusted, these adjustments being repeated until proper operation over the band is secured. When thus adjusted the system produces substantially constant voltage between the control electrode and cathode of the converter throughout the range of frequencies to be received and this is true notwithstanding the more emcient transfer of voltage to the control electrode through the network I5, I6 at the high frequencies than at the low frequencies.

Of course, while in the drawing I have represented the various inductances in the conventional form of coils, in actual practice these inductances may be of any desired form. It has been found that the inductances I0 and Il may comprise merely the inductances of certain lengths of straight wire. In one device constructed in accordance with my invention the inductance I0 comprised a wire of about an inch in length and the inductance II comprised a wire of about two inches in length. The arrangement which I have described possesses very desirable advantages when utilized at high frequencies such as those mentioned and are also very useful and desirable at lower frequencies.

While I have shown a particular embodiment of my invention, it will be understood that I do not wish to be limited thereto since different modifications may be made both in the circuit arrangements and in the instrumentalities employed and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination, in a frequency converter for high frequency receivers, of a signal input circuit, a tuned local oscillator circuit, said circuits including an inductive impedance in common, a tuning condenser in the local oscillator circuit in series with said impedance, and means for increasing the current in the impedance as the capacity of said tuning condenser increases thereby to increase the voltage supplied from the local oscillator to said signal input circuit as the frequency of the local oscillator is reduced.

2. The combination, in a frequency converter for high frequency receivers, of a signal input circuit, a tuned local oscillator circuit, said circuits including an inductive impedance in common, a tuning condenser in the local oscillator circuit in series with said impedance, said oscillator having a tendency to produce oscillations reducing in intensity as the capacity of said tuning condenser is increased to reduce the frequency of oscillations produced, and means utilizing the reduced impedance of said tuning con denser for increasing the current in said impedance thereby to maintain the voltage supplied from said oscillator to said signal input circuit within a narrow range of variation over the range of frequencies controlled by said tuning condenser.

3. The combination, in a frequency converter for high frequency receivers, of a signal input circuit, a local oscillator circuit, said circuits having two series connected impedances in common, means to tune said local oscillator circuit over a range of frequencies, the voltage on one of said impedances tending to vary during such tuning, and means to vary the voltage on the other of said impedances to compensate for variations in voltage produced on said one impedance during such tuning thereby to maintain the voltage supplied to said input circuit within a narrow range of variation.

4. The combination, in a frequency converter for high frequency receivers, of a signal input circuit, a local oscillator circuit having two series connected impedances and a variable tuning condenser, the voltage on one of said impedances varying as the tuning of said circuit is varied by variation of said tuning condenser, means to vary the voltage on the other of said impedances in response to variation of said tuning condenser to compensate for variation in voltage on said one impedance, and means to supply the combined voltage of said two impedances to said input circuit.

5. In combination, an electron discharge device having an anode, a cathode, and a control electrode, an inductance between said anode and control electrode having an intermediate point connected to said cathode, a plurality of condensers connected between said control electrode and points on said inductance between said anode and cathode, the condenser connected nearest the anode being variable over a range of frequencies whereby said device generates oscillations at a frequency determined by said condenser, and an output circuit for the oscillations produced connected between said anode and a point on said inductance.

6. In combination, an electron discharge converter having a tuned input circuit variable over a range of frequencies connected between its input electrodes, a local oscillator having a fre quency determining circuit tunable in unison with said tuned input circuit over a corresponding lower range of frequency whereby the percentage diiference in frequencies to which said circuits are tuned reduces as the frequency increases, the inductive and capacitive branches of said tuned input circuit being connected in series across an inductive impedance in said frequency determining circuit whereby voltage is supplied from said frequency determining circuit to said input electrodes, and means responsive to variation in tuning of said frequency determining circuit to vary the voltage on said inductive impedance to maintain substantially constant the voltage between said electrodes notwithstanding increased step-up of voltage by action of said inductive and capacitive branches when said percentage diiference in frequencies of said circuits is reduced.

7. In combination, an electron discharge converter having a tuned input circuit connected between its cathode and input electrode, a local electron discharge oscillator having an anode, a cathode, and a control electrode, said anode being connected to said control electrode through an oscillatory circuit comprising shunt connected inductance and variable capacity and to said cathode of said converter, said input electrode of said converter being connected through the inductance of said tuned input circuit to an intermediate point on said oscillatory circuit, and means responsive to variation of said variable capacity to maintain constant voltage from said local oscillator between said input electrode and cathode of said converter over a wide range of frequencies to which said circuits may be tuned.

8. In combination, an oscillating circuit including a variable tuning condenser, a load circuit, said oscillating circuit being arranged to supply oscillations to said load circuit, an inductive impedance common to said circuits, said oscillating circuit having a tendency to produce oscillations undesirably reducing in intensity as the capacity of said tuning condenser is increased to reduce the frequency of oscillations produced, and means for increasing the current in said impedance as the capacity of said tuning condenser increases thereby to vary the voltage supplied from said oscillating circuit to said load circuit in a sense to compensate for the undesirable reduction in intensity of said oscillations as the frequency of said oscillating circuit is reduced.

WILLIAM W. MOE. 

